An ideal diode should be very low-Ohmic for currents in forward direction and block current in reverse direction. A well-known circuit to achieve this is an active diode implemented by a large pass-transistor which is controlled by an amplifier. In order to have a low-Ohmic forward conduction, the pass transistor must be very large. The gate of this large pass-transistor is the load of the amplifier. An amplifier that has a fast response while driving a large capacitive load usually consumes a significant amount of power. Another option is to replace the amplifier with a comparator, but that may cause instability because when the comparator switches the pass transistor ON, switch resistance drops and as a result the voltage drop across the switch also drops and the comparator turns the switch OFF, switch resistance increases, increasing the voltage drop switch and so on.
US2016241225 discloses an active diode circuit for letting current pass in one direction and for blocking current in the opposite direction wherein the active diode circuit comprises a transistor, a control voltage generation circuit for generating a control voltage that is supplied to a control terminal of the transistor, and a sensing circuit for detecting a quantity indicative of a current flowing through the transistor, wherein the control voltage generation circuit generates the control voltage based on the detected quantity. The idea behind this current controlled active diode is to operate the transistor as a switch if forward current is above a certain threshold and drive it by the amplifier if current is below that threshold. However, it still has the drawback of having an amplifier driving the large pass transistor (at least during the moments when forward current is below the threshold).
0.5-V Input Digital Low-Dropout Regulator (LDO) with 98.7% Current Efficiency in 65 nm CMOS, EICE TRANS. ELECTRON., VOL. E94-C, NO. 6 Jun. 2011 by Yasuyuki Okuma, Koichi Ishida, Yoshikatsu Ryu, Xin Zhang, Po-Hung Chen, Kazunori Watanabe, Makoto Takamiya and Takayasu Sakura discloses a digital LDO including a switch array, a comparator controller (a serial-in parallel-out bi-directional shift register), and a digital controller wherein the comparator controller monitors the output voltage of the LDO and wherein the number of turned on switches is changed digitally by the digital controller based on the monitoring performed by the comparator controller.